Earlier this week I reported on how we may be experiencing the beginnings of a mobile bandwidth drought, with problems already being seen in densely populated areas during peak usage times. For the full details, check out the original report here. I contacted the three major U.S. carriers for the story, but didn't hear back from them before it was time for the story to run (and PCWorld even delayed the story for a week to give them more time to respond).

I've now heard back from Sprint and AT&T about the issues raised by my initial story. Both offered thoughtful and candid responses, and I appreciate the effort that went into tracking down answers to my questions. Still no word from Verizon.

AT&T was especially keen to respond to the points raised about their reputation for dropped calls and spotty service that, at one point, was so common that it was a running joke in pop culture. Spokeperson Stephen Schwadron was quick to tout the company's recent improvements to their network.

"Today, we have the nation's fastest mobile broadband network," claims Schwadron. "We've invested $75B to upgrade our wireline and wireless networks over the past 4 years--more than any other public company has invested in the United States.

However, AT&T does acknowledge some network troubles. Schwadron notes that the United States leads the world in mobile broadband use and AT&T leads all other U.S. companies in supporting more smartphones (not just the iPhone).

"In the last four years, we've seen mobile data traffic surge 8,000 percent and we expect traffic to grow eight to ten times 2010 levels by 2015... this unprecedented tidal wave of growth has caused challenges, particularly in large cities like New York and San Francisco." Schwadron admits. "AT&T is facing a spectrum crunch more severe and sooner than anyone else in the industry because we've been at the forefront of supporting skyrocketing mobile broadband usage."

Sprint spokesperson Kelly Schlageter confirmed to me that some cell sites are operating close to the 80 percent of capacity level cited in a Credit Suisse report issued last month. She also confirmed the belief of one of the experts I interviewed for my initial report that the capacity problem is not equally distributed across the network. She says while some towers are overwhelmed, others "are at 50% or even lower."

"That said," Schlageter continues, "Sprint has seen significant growth in data usage, upwards of 100% year-over-year. This is largely due to the success of iconic devices such as the HTC EVO and EVO 3D and Sprint's unlimited data plans."

In my story I also speculated that U.S. carriers seemed to be addressing issues around bandwidth scarcity by doing a little of everything, from trying to acquire more spectrum to building out networks and implementing data caps. The carriers I heard from seemed to confirm that's how they're looking at the problem, but AT&T's Schwadron clarified that for his company, there's really one paramount solution:

"Ultimately however, we are working with a finite spectrum resource," he says. Adding that the move to acquire T-Mobile is indeed viewed by AT&T as a play for more capacity. "The merger with T-Mobile provides by far the most effective, efficient, and immediate solution to address both companies network capacity challenges AND it creates network capacity beyond the sum of what each company could have created independently," Schwadron explains.

And one other thing - as for those pesky data caps, AT&T's Schwadron prefers to think of them as "tier pricing" that offers customers more choices better suited to their level of usage and budget. That's all true, but it's tough to overlook the omission of an "unlimited" package.

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